A combination of closely associated positive and negative cis-acting promoter elements regulates transcription of the skeletal alpha-actin gene.
The chicken skeletal alpha-actin gene promoter region provides at least a 75-fold-greater transcriptional activity in muscle cells than in fibroblasts. The cis-acting sequences required for cell type-restricted expression within this 200-base-pair (bp) region were elucidated by chloramphenicol acetyltransferase assays of site-directed Bg/II linker-scanning mutations transiently transfected into primary cultures. Four positive cis-acting elements were identified and are required for efficient transcriptional activity in myogenic cells. These elements, conserved across vertebrate evolution, include the ATAAAA box (-24 bp), paired CCAAT-box-associated repeats (CBARs; at -83 bp and -127 bp), and the upstream T+A-rich regulatory sequence (at -176 bp). Basal transcriptional activity in fibroblasts was not as dependent on the upstream CBAR or regions of the upstream T+A-rich regulatory sequence. Transfection experiments provided evidence that positive regulatory factors required for alpha-actin expression in fibroblasts are limiting. In addition, negative cis-acting elements were detected and found closely associated with the G+C-rich sequences that surround the paired CBARs. Negative elements may have a role in restricting developmentally timed expression in myoblasts and appear to inhibit promoter activity in nonmyogenic cells. Cell type-specific expression of the skeletal alpha-actin gene promoter is regulated by combinatorial and possibly competitive interactions between multiple positive and negative cis-acting elements.
Chow
K L
KL
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.
Schwartz
R J
RJ
D000199:Actins / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D002645:Chickens; D005786:Gene Expression Regulation; D005796:Genes; D005809:Genes, Regulator; D006801:Humans; D008969:Molecular Sequence Data; D009132:Muscles / Q000378:metabolism*; D009154:Mutation; D010957:Plasmids; D011401:Promoter Regions, Genetic; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic; D014162:Transfection
D000199:Actins